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IB Physics HL C 5 1 Doppler Effect Questions

Explain the Doppler effect and use relative source-observer motion to analyse observed frequency, wavelength, wavefronts and red-shift.

Syllabus
First assessment 2025
Course
Physics HL
Level
HL

Exam points

  • define the Doppler effect as a change in observed frequency caused by relative motion between a source and an observer
  • explain how source or observer motion changes wavefront spacing and observed frequency while wave speed in the medium remains fixed
  • interpret Doppler frequency shifts using source-observer direction, closest approach, wavefront diagrams and time graphs, including sound and red-shift evidence

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Study C.5.1—Doppler effect conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Physics HL C 5 1 Doppler Effect Questions question 1

[Maximum number: 2]

Two loudspeakers, A and B, are driven in phase and with the same amplitude at a frequency of 850 Hz . Point P is located 22.5 m from A and 24.3 m from B. The speed of sound is 340 ms−1340 \mathrm{~ms}^{-1}.

Figure for Question IB Physics HL C 5 1 Doppler Effect Questions question 1 — IB Physics HL

In another experiment, loudspeaker A is stationary and emits sound with a frequency of 850 Hz . The microphone is moving directly away from the loudspeaker with a constant speed v. The frequency of sound recorded by the microphone is 845 Hz .

Explain why the frequency recorded by the microphone is lower than the frequency emitted by the loudspeaker.

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